There are two conventional methods of impregnating a porous body with a molten alloy: (1) According to one method, which is called the autoclave process, a porous body is impregnated with molten metal under vacuum in a pressure vessel and then, under elevated pressures exerted by various gases, further impregnated with said molten metal. (2) According to the other method, a vacuum capsule holding a porous body sealed therein is submerged in the molten metal of a metal mold and then, under elevated pressure, said capsule is broken.
Method (1) calls for high temperatures (800.degree. - 1000.degree.C) and high pressures (1000 - 2000 atm.). The facilities to withstand these conditions have to be large and expensive and mass production is impossible. Moreover, there is a risk that the pressure vessel will burst. Method (2), involves the difficulty of sealing the porous body into a vacuum capsule, and is also unfit for mass production.